KR101046281B1 - Amine Borane Synthesis - Google Patents

Abstract

A process for preparing amine boranes from alkali metal borohydrides and amine salts is disclosed. Alkali metal borohydride is reacted with 0.95 to 1.05 equivalents of amine salt in a solvent containing water and amine.

Description

Amine Borane Synthesis {SYNTHESIS OF AMINE BORANES}

The present invention relates generally to a process for preparing amine boranes from sodium borohydride and amine salts.

Processes for preparing amine boranes from sodium borohydride and amine salts are well known and the reaction is usually carried out in an organic solvent in which sodium borohydride is dissolved. For example, US Pat. No. 6,060,623 describes the preparation of amine boranes from sodium borohydride and amine salts in organic solvents such as 1,2-dimethoxyethane. In this method, the initial reaction mixture must be distilled to remove the solvent before separating the amine borane product.

The problem addressed by the present invention is to provide a more efficient process for producing amine boranes from sodium borohydride and amine salts without the use of additional solvents for borohydride starting materials.

The present invention relates to a process for preparing amine boranes from alkali metal borohydrides and amine salts. This process comprises alkali metal borohydride (i) an amine which is the base form of an amine salt; And (ii) reacting with 0.95 to 1.05 equivalents of the amine salt in a solvent comprising water, wherein the weight ratio of total water to alkali metal borohydride in the solvent is 0.5: 1 to 2.7: 1; The solvent contains up to 5% by weight of a solvent other than water and amine.

Unless stated otherwise, all percentages herein are stated in weight percent and temperature is ° C. Parts in parts per million (ppm) are by weight / volume. When alkali metal borohydride is added as the dihydrate, the ratio of the amounts to the amount of alkali metal borohydride is relative to the contained alkali metal borohydride but not to the dihydrate.

An "alkyl" group is a saturated hydrocarbyl group having 1 to 20 carbon atoms and may be linear, branched or cyclic. In some embodiments of the invention, the alkyl groups are linear or branched, or optionally they are linear. In some embodiments, the alkyl group has 1 to 6 carbon atoms, or optionally 1 to 4 carbon atoms. A "hydrocarbon solvent" is essentially any material that contains only carbon and hydrogen and is liquid at a pressure of 100 kPa and 0 ° C. The hydrocarbon solvent may contain traces of elements other than carbon and hydrogen as impurities, for example, less than 0.5%. In some embodiments of the invention, the hydrocarbon solvent is an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon or a mixture thereof; Optionally, saturated aliphatic hydrocarbons and / or aromatic hydrocarbons, optionally C ₄ -C ₁₆ saturated aliphatic hydrocarbons and / or C ₇ -C ₂₀ aromatic hydrocarbons. Aromatic hydrocarbons contain aromatic rings and may have alkyl substituents. Particularly preferred hydrocarbon solvents include mineral oil, toluene, xylene, ethylbenzene, C ₆ -C ₁₆ saturated aliphatic hydrocarbons and mixtures thereof.

The reaction of an alkali metal borohydride with an amine is shown in general form in the following formula:

MBH ₄ + HA + R ₃ N → R ₃ NBH ₃ + MA + H ₂

Where

M represents an alkali metal cation;

A represents a base pair derived from mineral oil, boric acid or carbonic acid;

R may represent the same or different alkyl group and / or hydrogen, provided that at least two alkyl groups are present.

Preferably, the alkyl group is a C ₁ -C ₄ alkyl group, optionally methyl or ethyl. Preferably, R does not represent hydrogen and the amine is trialkylamine. Preferably, M is sodium or potassium. Preferably, the acid HA is hydrochloric acid or sulfuric acid. In some embodiments, the amine hydrochloride is pre-formed, wherein the formula is:

MBH ₄ + R ₃ NHA → R ₃ NBH ₃ + MA + H ₂

In these embodiments, free amine and water are added as solvents.

As used herein, solvent is present in embodiments where the amine salt is produced in situ from amines and acids, including any water present in the aqueous acid and any hydrated water from alkali metal borohydride. Includes all the water you do. Preferably, the weight ratio of water to alkali metal borohydride in the solvent is at least 0.7: 1, or at least 0.8: 1, or at least 0.9: 1, or at least 1: 1, or at least 1.5: 1; Preferably the ratio is at most 2.5: 1, or at most 2.2: 1, or at most 2: 1.

Preferably, the reaction takes place at a temperature in the range from 5 ° C. to less than 5 ° C. at atmospheric boiling point of the solvent. In some embodiments, the temperature is at least 10 ° C., or at least 15 ° C .; And preferably 100 ° C. or less, or 70 ° C. or less, or 50 ° C. or less.

In some embodiments of the invention, the solvent contains up to 5% of any solvent other than water and amine. In these embodiments, the weight ratio of total water to alkali metal borohydride in the solvent is preferably 0.5: 1 to 2.7: 1, or 0.8: 1 to 2.7: 1, or 1: 1 to 2.7: 1, or 1.5: 1 to 2.7: 1, or 1: 1 to 2.5: 1, or 1.5: 1 to 2.5: 1. In these embodiments, preferably the alkali metal borohydride is sodium borohydride introduced in its dihydrate form. In these embodiments, the weight ratio of free amine, ie, amine that is not in salt form to alkali metal borohydride, is 1: 1 to 6: 1, or 1.5: 1 to 6: 1, or 2: 1 to 6 : 1, or 2: 1 to 5: 1, or 2.5: 1 to 4.5: 1.

In some embodiments of the invention, the solvent further comprises a hydrocarbon solvent or a combination of hydrocarbon solvents. In these embodiments, preferably the weight ratio of total water to alkali metal borohydride is from 0.5: 1 to 2.5: 1, or from 0.5: 1 to 2: 1, or from 0.7: 1 to 2: 1, or from 0.7: 1 to 1.5: 1. In these embodiments, preferably the weight ratio of hydrocarbon solvent (s) to alkali metal borohydride is 1.5: 1 to 12: 1, or 2: 1 to 12: 1, or 2: 1 to 10: 1, or 1.5 : 1 to 8: 1. In these embodiments, preferably the hydrocarbon solvent (s) is from 25 wt% to 70 wt%, or from 30 wt% to 65 wt%, or from 30 wt% to 60 wt%, or from 35 wt% to the total weight of the reactants and solvent. 60% by weight. In these embodiments, the weight of the total amine, preferably as the amine contained in the free amine and the amine salt, is at least 20%, or at least 22%, or at least 24% by weight of the total weight of the reactants and the solvent; Preferably it is 40 weight% or less, or 36 weight% or less, or 34 weight% or less. In these embodiments, the weight of the total water, preferably as water contained in the free water and the aqueous acid or hydrate, is at least 5%, or at least 6%, or at least 7%, or at least 8% by weight of the reactants and the solvent. weight%; And preferably 15% by weight or less, or 14% by weight or less, or 13% by weight or less, or 12% by weight or less.

Preferably, the solvent contains 5% or less, or 2% or less, of a solvent in which the alkali metal borohydride is dissolved at least about 2%. The solvent in which the alkali metal borohydride is dissolved includes C ₃ -C ₈ aliphatic amine, C ₃ -C ₈ cyclic amine, C ₃ -C ₈ diamine, C ₃ -C ₈ alkanolamine, C ₅ -C ₁₀ aromatic amine, C ₄ -C ₁₂ methyl ethers and C ₂ -C ₈ amides of ethylene glycol and ethylene glycol oligomers. Aliphatic amines include mono-, di- and tri-alkyl amines, in particular mono-alkyl amines, in particular primary and secondary mono-alkyl amines. Aromatic amines include pyridine. Optimal amide solvents include N, N-dialkyl amides, especially aliphatic amides. Commonly used solvents include n-propylamine, isopropylamine, isobutylamine, sec-butylamine, n-butylamine, n-pentylamine, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, pyridine, Dimethylformamide and dimethylacetamide.

Example

Solid sodium in toluene at room temperature With borohydride  solid Triethylamine  Hydrochloride ( NEt ₃ HCl )

A three-necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 grams of SBH AF Grans (SBH with particle size greater than 80 mesh and less than 40 mesh). Then 100 mL of anhydrous toluene and 30 mL of NEt ₃ were added. This slurry was stirred and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added. No gas was released during the addition. The reaction was stopped. no response; Yield = 0%.

Isopropylamine  Sodium Borohydride  And solid NEt ₃ HCl

A three necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 grams SBH AF Grans, 90 grams of isopropylamine and 50 mL of triethylamine. The resulting solution was stirred and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added over 3 hours. The addition of solid NEt ₃ HCl produced gas immediately. After the addition was complete, the slurry was stirred for another 3 hours at which time 50 mL of deionized water was added. The resulting biphasic solution was placed in a separatory funnel. Both isopropylamine and water phases were analyzed by ¹ H and ¹¹ B NMR. The isopropylamine upper layer contained 98% NH ₂ ⁱ PrBH ₃ and 2% NEt ₃ BH ₃ .

Synthetic sodium Borohydride 2 hydrates  100 mL  Toluene and solid NEt ₃ HCl

A three necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 g SBH AF Grans, 10 g water and 0.1 g NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 100 mL of anhydrous toluene and 30 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 100 mL of fresh toluene. All toluene phases were combined. Both toluene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.0 g water 10.0 g NEt ₃ 25 g toluene 100 mL (86.5 g) 123.76 g NEt ₃ HCl 36.2 g Added water 60 mL (60 g) 87.88 g Toluene Cleaning 1 100 mL (86.5 g) 56.5 g Toluene Cleaning 2 100 mL (86.5 g) 70.50 g Toluene Cleaning 3 100 mL (86.5 g) 100.27 g 383.03 g yield 98%

Synthetic sodium Borohydride 2 hydrates  50 mL  Toluene and solid NEt ₃ HCl

A three necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 g of SBH AF Grans and 10 g of water and 0.1 g of NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 50 mL of anhydrous toluene and 10 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.3 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 30 mL of fresh toluene. All toluene phases were combined. Both toluene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.0 g water 10.0 g NEt ₃ 10 mL (7.26 g) toluene 50 mL (43.5 g) 73.25 g NEt ₃ HCl 36.3 g Added water 60 mL (60 g) 82.43 g Toluene Cleaning 1 30 mL (25.95 g) 26.89 g Toluene Cleaning 2 30 mL (25.95 g) 19.90 g Toluene Cleaning 3 30 mL (35.95 g) 25.74 g 145.77 g yield 98%

Synthetic sodium Borohydride 2 hydrates  50 mL of Dodecane  And solid NEt ₃ HCl  (A small amount of NEt ₃ HCl  adding)

A three-necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 g of SBH AF Grans, 10 g of water and 0.1 g of NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 50 mL of anhydrous dodecane and 10 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (26.4 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 30 mL of fresh toluene. All toluene phases were combined. Both dodecane and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.16 g water 10.0 g NEt ₃ 10 mL (7.26 g) Dodecane 50 mL (37.5 g) 65.15 g NEt ₃ HCl 26.4 g Added water 60 mL 73.21 g Dodecane Cleaning 1 30 mL (22.5 g) 21.20 g Dodecane Cleaning 2 30 mL (22.5 g) 23.37 g Dodecane Cleaning 3 30 mL (22.5 g) 27.80 g 137.50 g yield 44%

KBH ₄  And 50 mL Toluene and Solids NEt ₃ HCl

A three-necked flask with a solid addition funnel, thermometer, and nitrogen gas purge was charged with 14.21 g KBH ₄ 100 and 10 g water and 0.1 g NaOH. Then 50 g of anhydrous toluene and 10 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 30 mL of fresh toluene. All toluene phases were combined. Both toluene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery KBH ₄ 100 14.21 g water 10 g NEt ₃ 10 mL (7.26 g) toluene 50 mL (43.5 g) 69.52 g NEt ₃ HCl 36.2 g Added water 60 mL (60 g) 88.85 g Toluene Cleaning 1 30 mL (25.95 g) 20.96 g Toluene Cleaning 2 30 mL (25.95 g) 21.82 g Toluene Cleaning 3 30 mL (25.95 g) 27.34 g 139.64 g yield 93%

Synthetic sodium Borohydride 2 hydrates  25 mL Toluene and Solids NEt ₃ HCl

A three necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 g of SBH AF Grans and 10 g of water and 0.1 g of NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 25 mL of anhydrous toluene and 5 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 30 mL of fresh toluene. All toluene phases were combined. Both toluene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.16 g water 10.0 g NEt ₃ 5 mL (3.63 g) toluene 25 mL (21.62 g) 49.29 g NEt ₃ HCl 36.2 g Added water 60 mL 72.44 g 72.44 g Toluene Cleaning 1 15 mL (12.97 g) 16.15 g Toluene Cleaning 2 15 mL (12.97 g) 16.16 g Toluene Cleaning 3 15 mL (12.97 g) 16.23 g 97.81 g yield 98%

Synthetic sodium Borohydride 2 hydrates  25 mL Of xylene and solid NEt ₃ HCl

A three necked flask with a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 g of SBH AF Grans and 10 g of water and 0.1 g of NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 25 mL of anhydrous xylene and 5 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 x 30 mL of fresh xylene. All xylene phases were combined. Both xylene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.10 g water 10.0 g NEt ₃ 5 mL (3.63 g) Xylene 25 mL (21.5 g) 48.56 g NEt ₃ HCl 36.2 g Added water 60 mL 61.19 g 61.19 g Xylene Cleaning 1 15 mL (12.9 g) 17.70 g Xylene Cleaning 2 15 mL (12.9 g) 7.29 g Xylene Cleaning 3 15 mL (12.9 g) 5.17 g 78.75 g yield 98%

Synthetic sodium Borohydride 2 hydrates  25 mL of Triethylamine  And solid NEt ₃ HCl

A three-necked flask with a solid addition funnel, thermometer, and nitrogen gas purge was charged with 10 g ram SBH AF Grans and 10 g water and 0.1 g NaOH. The slurry was stirred for 24 hours until a solid mass formed. Then 25 mL of anhydrous triethylamine were added. The slurry was stirred so that the reaction temperature did not rise above 40 ° C, and 1 equivalent of solid NEt ₃ HCl (36.2 g) was added.

When the reaction temperature rose above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting biphasic solution was placed in a separatory funnel and the bottom phase was washed with 3 × 5 mL of fresh NEt ₃ . All triethylamine phases were combined. Both triethylamine and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.10 g water 10.0 g NEt ₃ 25 mL (18.15 g) 33.52 g NEt ₃ HCl 36.2 g Added water 60 mL 55.0 g 55.0 g NEt ₃ cleaning 1 5 mL (3.63 g) 0.55 g NEt ₃ cleaning 2 5 mL (3.63 g) 2.92 g NEt ₃ Cleaning 3 5 mL (3.63 g) 3.19 g 40.18 g yield 96%

Synthetic sodium Borohydride 2 hydrates  100 mL Of toluene and preformed NEt ₃ HCl

A three-necked flask containing a solid addition funnel, thermometer and nitrogen gas purge was charged with 10 grams of SBH AF Grans, 10 grams of water and 0.1 grams of NaOH. The slurry was stirred for 24 hours until a solid mass formed. Another three necked flask was charged with one equivalent of NEt ₃ and one equivalent of 37% HCl. Then 100 mL of anhydrous toluene and 30 mL of NEt ₃ were added. The slurry was stirred so that the reaction temperature did not increase above 40 ° C. and the contents of the first flask were added.

When the reaction temperature increased above 30 ° C., a large amount of gas was released. After 6 hours, 60 mL of water was added to dissolve all the solids in the reaction pot. The resulting two phase solution was placed in a separatory funnel and the lower phase was washed with 3 x 100 mL of fresh toluene. All toluene phases were combined. Both toluene and water phases were analyzed by ¹ H and ¹¹ B NMR.

Filling material Charge Recovery Total recovery SBH AF Grans 10.30 g water 10.0 g NEt ₃ 86.5 mL (62.80 g) toluene 50 mL (43.25 g) 105.97 g 39% HCl 21.74 mL Added water 60 mL (60 g) 105.74 g Toluene Cleaning 1 100 mL (86.5 g) 86.17 g Toluene Cleaning 2 100 mL (86.5 g) 77.86 g Toluene Cleaning 3 100 mL (86.5 g) 78.64 g 348.64 g yield 54%

The following table summarizes the above experiments and results.

Table 1: Synthesis of NEt ₃ BH ₃ (1)

menstruum g Excess added NEt ₃ , mL SBH content, g SBH form NEt ₃ HCl Form of NEt ₃ HCl Washing, mL Reaction temperature ℃ NEt ₃ BH ₃ yield% by NMR Isopropyl amine 90 50 10 Pure form 1 equivalent solid 0 22 2 toluene 100 50 10 Pure form 1 equivalent solid 0 22 0 toluene 100 25 10 2H ₂ O 1 equivalent solid 3 × 100 22-40 98 toluene 50 10 10 2H ₂ O 1 equivalent solid 3 × 30 22-40 98 Dodecane 50 25 10 2H ₂ O 0.72 equivalent solid 3 × 30 22-40 54 toluene 50 25 14.21 KBH ₄ 1 equivalent solid 3 × 30 22-40 93 toluene 25 5 10 2H ₂ O 1 equivalent solid 3 × 15 22-40 98 Xylene 25 5 10 2H ₂ O 1 equivalent solid 3 × 15 22-40 98 NEt ₃ 25 0 10 2H ₂ O 1 equivalent solid 3 × 5 22-40 96 NEt ₃
SBH-
NEt ₃ HCl 50 21.71 10 2H ₂ O 1 equivalent Preform 3 × 100 22-40 54

Additional experimental results are summarized in the following table.

Borohydride MBH4, g Addition method mountain Concentration of acid Reaction temperature yield NaBH ₄ * 2H ₂ O 10 Acid addition HCl 37 wt% Room temperature to 40 ℃ 97 NaBH ₄ * 2H ₂ O 10 Preform HCl 37 wt% Room temperature to 40 ℃ 98 NaBH ₄ * 2H ₂ O 10 Acid addition H ₂ SO ₄ 98 wt% Room temperature to 40 ℃ 0 NaBH ₄ * 2H ₂ O 100 Acid addition HCl 37 wt% Room temperature to 40 ℃ 80 NaBH ₄ * 2H ₂ O 50 Acid addition HCl 37 wt% Room temperature to 40 ℃ 74 NaBH ₄ * 2H ₂ O 50 Preform HCl 37 wt% Room temperature to 40 ℃ 85 NaBH ₄ * 2H ₂ O 50 Preform HCl 37 wt% 8 ℃ to 20 ℃ 64 KBH ₄ 12.25 Acid addition HCl 9.25 wt% Room temperature to 40 ℃ 55 KBH ₄ 12.25 Acid addition HCl 17.5 wt% Room temperature to 40 ℃ 85 KBH ₄ 12.25 Acid addition HCl 37 wt% Room temperature to 40 ℃ 65 (18 hours) KBH ₄ 12.25 Acid addition HCl 37 wt% Room temperature to 40 ℃ 61 (6 hours) KBH ₄ 12.25 Acid addition H ₂ SO ₄ 75 wt% Room temperature to 40 ℃ 79 KBH ₄ 12.25 Acid addition H ₂ SO ₄ 50 wt% Room temperature to 40 ℃ 51 KBH ₄ 12.25 g Acid addition H ₂ SO ₄ 25 wt% Room temperature to 40 ℃ 44 Plant generation
NaBH ₄ * 2H ₂ O 20 Acid addition HCl 37 wt% Room temperature to 35 ° C 68 Plant generation
NaBH ₄ * 2H ₂ O 20 Preform HCl 37 wt% Room temperature to 35 ° C 62 synthesis
NaBH ₄ * 2H ₂ O 20 Preform HCl 37 wt% Room temperature to 35 ° C 71

RT = room temperature, ie 20-25 ° C.

Claims (6)

Alkali metal borohydrides are (i) free amines which are the base form of an amine salt; And (ii) reacting with 0.95 to 1.05 equivalents of amine in a solvent comprising water, Wherein the weight ratio of total water to alkali metal borohydride is from 0.5: 1 to 2.7: 1; A solvent for producing amine borane from alkali metal borohydride and amine salts, wherein the solvent contains up to 5% by weight of solvents other than water and amine. The method of claim 1 wherein the weight ratio of total water to alkali metal borohydride in the solvent is 1: 1 to 2.7: 1. The method of claim 2 wherein the amine salt is a trialkylamine salt. 4. The process of claim 3 wherein the weight ratio of free amine to alkali metal borohydride is 1: 1 to 6: 1. The method of claim 4 wherein the alkali metal borohydride is sodium borohydride added in the form of a dihydrate. The method of claim 4 wherein the alkali metal borohydride is potassium borohydride.